The present invention relates to an electro-optic device and, more particularly, to an electro-optic window having enclosed therein at least one photovoltaic device.
Heretofore, devices of reversibly variable transmittance to electromagnetic radiation have been proposed for such applications as the variable transmittance element in variable transmittance light-filters, variable reflectance mirrors, and display devices which employ such light-filters or mirrors in conveying information. These variable transmittance light filters have included windows. Among such devices are those where the transmittance is varied by thermochromic, photochromic, or electro-optic (e.g., liquid crystal, dipolar suspension, electrophoretic, electrochromic, etc.) means and where the variable transmittance characteristic affects electromagnetic radiation that is at least partly in the visible spectrum (wavelengths from about 3800 .ANG. to about 7600 .ANG.). Typically, proposed control schemes for variable transmittance windows either allow the windows to be power controlled window-by-window with a person determining when the window should darken or have all windows controlled by a central computerized power source such that the window is darkened when the sun shines on them or on a sensor placed on a particular side of a building.
Devices of reversibly variable transmittance to electromagnetic radiation, wherein the transmittance is altered by electrochromic means are described, for example, by Chang, "Electrochromic and Electrochemichromic Materials and Phenomena," in Non-emissive Electrooptic Displays, A. Kmetz and K. von Willisen, eds. Plenum Press, New York, N.Y., pp. 155-196 (1976) and in various parts of Eletrochromism, P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCH Publishers, Inc., New York, N.Y. (1995). Numerous electrochromic devices are known in the art. See, e.g., Manos, U.S. Pat. No. 3,451,741; Bredfeldt et al., U.S. Pat. No. 4,090,358; Clecak et al., U.S. Pat. No. 4,139,276; Kissa et al., U.S. Pat. No. 3,453,038; Rogers, U.S. Pat. Nos. 3,652,149, 3,774,988 and 3,873,185; and Jones et al., U.S. Pat. Nos. 3,282,157, 3,282,158, 3,282,160 and 3,283,656.
In addition to these devices there are commercially available electro-optic devices and associated circuitry, such as those disclosed in U.S. Pat. No. 4,902,108, entitled "Single-Compartment, Self-Erasing, Solution-Phase Electro-optic Devices Solutions for Use Therein, and Uses Thereof", issued Feb. 20, 1990 to H. J. Byker; Canadian Patent No. 1,300,945, entitled "Automatic Rearview Mirror System for Automotive Vehicles", issued May 5, 1992 to J. H. Bechtel et al.; U.S. Pat. No. 5,128,799, entitled "Variable Reflectance Motor Vehicle Mirror", issued Jul. 7, 1992 to H. J. Byker; U.S. Pat. No. 5,202,787, entitled "Electro-Optic Device", issued Apr. 13, 1993 to H. J. Byker et al.; U.S. Pat. No. 5,204,778, entitled "Control System For Automatic Rearview Mirrors", issued Apr. 20, 1993 to J. H. Bechtel; U.S. Pat. No. 5,278,693, entitled "Tinted Solution-Phase Electrochromic Mirrors", issued Jan. 11, 1994 to D. A. Theiste et al.; U.S. Pat. No. 5,280,380, entitled "UV-Stabilized Compositions and Methods", issued Jan. 18, 1994 to H. J. Byker; U.S. Pat. No. 5,282,077, entitled "Variable Reflectance Mirror", issued Jan. 25, 1994 to H. J. Byker; U.S. Pat. No. 5,282,077, entitled "Variable Reflectance Mirror", issued Jan. 25, 1994 to H. J. Byker; U.S. Pat. No. 5,294,376, entitled "Bipyridinium Salt Solutions", issued Mar. 15, 1994 to H. J. Byker; U.S. Pat. No. 5,336,448, entitled "Electrochromic Devices with Bipyridinium Salt Solutions", issued Aug. 9, 1994 to H. J. Byker; U.S. Pat. No. 5,434,407, entitled "Automatic Rearview Mirror Incorporating Light Pipe", issued Jan. 18, 1995 to F. T. Bauer et al.; U.S. Pat. No. 5,448,397, entitled "Outside Automatic Rearview Mirror for Automotive Vehicles", issued Sep. 5, 1995 to W. L. Tonar; and U.S. Pat. No. 5,451,822, entitled "Electronic Control System", issued Sep. 19, 1995 to J. H. Bechtel et al. Each of these patents is commonly assigned with the present invention and the disclosures of each, including the references contained therein, are hereby incorporated herein in their entirety by reference.
Photoelectrochromism is discussed generally in pages 192-197 of Eletrochromism, P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCH Publishers, Inc., New York, N.Y. (1995). Specifically, section 12.2.3, entitled "Cells Containing Photovoltaic Materials", discusses how a photovoltaic material produces a potential when illuminated and where the photovoltaic material has an internal rectifying field which provides a driving force for the electrons. This section goes on to describe that the voltage created by the photovoltaic material is insufficient, by itself, to darken the electrochromic material. Therefore the electrochromic cell incorporating a photovoltaic material needs an external bias applied which is supplemented by the small photovoltaic-voltage to cause electron transfer to proceed, i.e., have the electrochromic material darken.
U.S. Pat. No. 5,377,037, entitled "Electrochromic-Photovoltaic Film for Light-Sensitive control of Optical Transmittance" to H. M. Branz et al. teaches a variable transmittance optical component which includes a solar cell-type photovoltaic device. The photovoltaic material is deposited over the entire surface of a transparent electrically conductive layer section. The photovoltaic material includes a p-type hydrogenated silicon carbide section, an undoped hydrogenated silicon carbide section, and phosphorous-doped hydrogenated silicon carbide section. A standard solid-state electrochromic multilayer structure is then deposited over the layer of photovoltaic material such that the light traveling through the optical transmitter must travel through the photovoltaic material and through the electrochromic material. The photovoltaic material will absorb some portion of the light and will also create sufficient current to darken the electrochromic material. Solid-state electrochromic devices with good memory, once darkened, will not clear or bleach quickly without an external method of closing the electrochemical circuit, i.e., the device will not clear in a reasonable time even though the "darkening potential" is removed. The device taught by Branz et al. attempts to overcome this significant limitation by connecting a bleeder resistor to the two transparent conductive electrode layers to provide the electric potential and circuit across the device (to slowly bleach the device). In operation, the photovoltaic device produces a DC current which is applied between the transparent conductive layers and across the bleeder resistor. However, it takes a light source with the intensity of 1-2 suns to produce a transmission drop of only 10 percent, in approximately 12-13 minutes. Thus, incorporating a bleeder resistor complicates the circuitry required for the window system and also draws some power that otherwise could be used in darkening.
U.S. Pat. No. 5,348,653, entitled "Stand-Alone Photovoltaic (PV) Powered Electrochromic Window" to D. K. Benson et al. teaches a variable transmittance double pane window including a five-layer solid state electrochromic portion, an array of photovoltaic cells with a n-type conductivity region on the front side of a p-type silicon substrate, and an external switch-containing circuit. The photovoltaic cells are deposited directly on the glass and not on the transparent electrode. The photovoltaic cells and the battery circuit are connected in parallel to the electrochromic portion of the device. This allows selective activation of the electrochromic portion to either a substantially opaque state or a substantially transparent state by switching the external switch-containing circuit between having the photovoltaic devices drive the device to a dark state, or to a transparent state or having the battery device drive the device to a transparent state when the conditions are such that the incident sunlight is not sufficient for the photovoltaic array to produce the required energy. Again, solid-state electrochromic devices with good memory, once darkened, will not clear in a reasonable amount of time absent some method of closing the circuit, typically by applying a bleaching potential.
U.S. Pat. No. 5,457,564, entitled "Complementary Surface Confined Polymer Electrochromic Materials, Systems, and Methods of Fabrication Therefore" to Leventis et al. teaches an electrochromic device having polypyrrole-prussian blue composite material on the oxidatively coloring electrode and a heteroaromatic substance with at least one quaternized nitrogen on the reductively coloring electrode. Preferably, either the oxidative or reductive polymer is electro-deposited onto a metallic oxide to increase the cycle life of the device to an acceptable level. Leventis et al. also teaches using an external photovoltaic cell to generate power to darken the electrochromic device. The photovoltaic cells operate as forward biased diodes and allow current to flow in the opposite or "reverse" direction. Further, Leventis et al. places the photovoltaic cells behind the electrochromic device such that the light which drives them must first travel through the electrochromic material. As the degree of colorization of the device increases, the intensity of light impinging on the photovoltaic cells decreases and the output from the photovoltaic cells decreases, creating a limit of how much light the device can block.
When retrofitting windows it is disadvantageous to have to run wires to each window to supply the external bias. Furthermore, even when installing electrochromic windows into a new building it would be easier and less expensive if no wires were needed to supply an external bias or no external circuit were necessary to help control colorization or bleaching of the window.
Consequently, it is desirable to provide an improved electro-optic window having an improved photovoltaic drive mechanism.